1. Technical Field
The present invention relates to a screen unit.
2. Related Art
A type of screen unit which expands a screen when the screen is used and winds and accommodates the screen when the screen is not used is known. An example of this type of screen unit currently proposed includes a screen which has a pair of crossing sides opposed in a direction crossing the winding direction of the screen (hereinafter referred to as a crossing direction as well) and curved toward the inside, pipe-shaped members provided on both the crossing sides, string-shaped members extended along the respective crossing sides and inserted into the pipe-shaped members, and a mechanism for giving tension to the respective string-shaped members in the directions along the respective crossing sides (for example, see JP-A-2009-229915).
According to the structure of this screen unit which gives tension to the respective string-shaped members in the directions along the crossing sides, the screen is tensioned not only in the screen winding direction but also in the crossing direction. Thus, the flatness of the screen increases.
According to this screen unit, however, the screen is damaged by the contact between the string-shaped members provided along the curved crossing sides of the screen and the base material of the screen in the winding condition of the screen. Moreover, under the winding condition, deformations such as depressions are produced on the base material of the screen by the steps produced by the string-shaped members.
For solving these problems, a screen unit proposed in JP-A-2009-229915 contains pipe-shaped members having sufficiently large lengths in the crossing direction such that the string-shaped members can be positioned outside the portions of the crossing sides having the largest width between the crossing sides. In this case, the string-shaped members do not overlap with the screen under the winding condition of the screen, thereby preventing damage and deformation of the base material of the screen.
According to this structure of the screen unit, the damage and deformation of the base material of the screen are avoided. However, since the string-shaped members are disposed farther outward from the crossing sides of the screen, the size of the screen unit increases. Moreover, the pipe-shaped members provided on both the crossing sides of the screen become longer in the crossing direction, which deteriorates the appearance of the screen in the expanded condition.